CN117457894A - Polycrystalline positive electrode material, preparation method thereof and lithium ion battery - Google Patents

Polycrystalline positive electrode material, preparation method thereof and lithium ion battery Download PDF

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CN117457894A
CN117457894A CN202311785185.7A CN202311785185A CN117457894A CN 117457894 A CN117457894 A CN 117457894A CN 202311785185 A CN202311785185 A CN 202311785185A CN 117457894 A CN117457894 A CN 117457894A
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positive electrode
electrode material
polycrystalline
doping element
polycrystalline positive
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CN117457894B (en
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刘晓明
高爽
胡平平
花彬昌
张媛媛
刘志远
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Ningbo Ronbay Lithium Battery Material Co Ltd
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Ningbo Ronbay Lithium Battery Material Co Ltd
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Abstract

The invention provides a polycrystalline positive electrode material, a preparation method thereof and a lithium ion battery. The polycrystalline positive electrode material includes: a core layer comprising oxides of Li, ni and doping elements; a cladding layer which coats at least part of the surface of the core layer, and which comprises oxides composed of Li, doping elements and cladding element L; wherein the doping elements comprise a heavy doping element A and a light doping element D; in the cladding layer, the doping element is obtained by outward diffusion of the doping element in the core layer; the polycrystalline positive electrode material has a radial structure, and the cross-sectional porosity of the polycrystalline positive electrode material ranges from 0.3% to 3%. According to the invention, the fine primary particles are more aggregated by pressurizing oxygen, so that the porosity is reduced, the polycrystalline positive electrode material is promoted to be in a high-density state, the compaction density of the polycrystalline positive electrode material is improved, the rate capability of the polycrystalline positive electrode material is improved, and the stability of the polycrystalline positive electrode material is further improved.

Description

Polycrystalline positive electrode material, preparation method thereof and lithium ion battery
Technical Field
The invention relates to the technical field of lithium ion batteries, in particular to a polycrystalline positive electrode material, a preparation method thereof and a lithium ion battery.
Background
Lithium ion (Li) + ) The battery is a secondary battery which mainly depends on Li + And moves between the positive electrode and the negative electrode to operate. During charge and discharge, li + To-and-fro intercalation and deintercalation between two electrodes: during charging, li + De-intercalation from the positive electrode, and intercalation into the negative electrode through the electrolyte, wherein the negative electrode is in a lithium-rich state; the opposite is true when discharging. Batteries generally employ materials containing lithium elements as electrodes, and lithium-containing positive electrode materials are representative of modern high-performance batteries.
In the research and development and preparation process of lithium ion batteries and positive electrode materials thereof, primary particles are mutually fused and become large, so that internal large gap residues are caused, and the problem of low circulation rate and stability of the lithium ion batteries is caused, so that how to improve the circulation rate and the low stability is always a target pursued by industry practitioners.
Disclosure of Invention
According to the polycrystalline positive electrode material, the preparation method thereof and the lithium ion battery, fine primary particles are gathered more by pressurizing oxygen, so that the porosity is reduced, the polycrystalline positive electrode material is promoted to be in a high-density state, the compaction density of the polycrystalline positive electrode material is improved, the rate capability of the polycrystalline positive electrode material is improved, and the stability of the polycrystalline positive electrode material is further improved.
To this end, a first object of the present invention is to provide a polycrystalline positive electrode material;
the second object of the present invention is to provide a method for preparing a polycrystalline cathode material;
a third object of the present invention is to provide a lithium ion battery;
to achieve the first object of the present invention, the present invention provides a polycrystalline cathode material comprising: a core layer comprising oxides of Li, ni and doping elements; a cladding layer which coats at least part of the surface of the core layer, and which comprises oxides composed of Li, doping elements and cladding element L; wherein the doping elements comprise a heavy doping element A and a light doping element D; the light doping element D includes at least one of F, na, mg, al, ca; the heavily doped element a includes at least one of Ti, mo, W, ta; the cladding element L includes at least one of Li, al, W, ti, zr, sr, B, F; in the cladding layer, the doping element is obtained by outward diffusion of the doping element in the core layer; the polycrystalline positive electrode material has a radial structure, and the cross-sectional porosity of the polycrystalline positive electrode material ranges from 0.3% to 3%.
Compared with the prior art, the technical effect achieved by adopting the technical scheme is as follows: the polycrystalline positive electrode material comprises a core layer and a coating layer, wherein the core layer comprises oxides composed of Li, ni and doping elements, and during the charge and discharge process of the lithium ion battery, li ions have higher energy density, power density, better cycle performance and reliable safety performance along with the deintercalation of the Li ions in the positive electrode material; the higher the Ni content, the higher the material capacity, and the better the battery performance; the doping elements comprise a heavy doping element A and a light doping element D, wherein the heavy doping element A is defined by the relative molecular mass of the elements being 40 (calcium element), when the relative molecular mass is smaller than the calcium element, the light doping element D is defined as the light doping element A, and when the relative molecular mass is larger than the calcium element, the light doping element A is defined as the heavy doping element A; the light doping element D includes at least one of F, na, mg, al, ca; the heavily doped element a includes at least one of Ti, mo, W, ta.
The higher the oxidation state of the dopant is, the better the cycle performance is improved, the high orientation is promoted, the slender microstructure, namely the radial structure, is formed, the integrity of the positive electrode material can be maintained, the increase of impedance is restrained, and the cycle performance is improved; therefore, in the preparation process of the polycrystalline positive electrode material, the primary particles are required to be prevented from being mutually fused by keeping a radial structure, and the currently adopted method is to form a coating layer on the outer surface by doping W, mo, nb, ta and other heavy elements which are not easy to enter the primary particles so as to prevent the primary particles from being mutually fused, thereby keeping the radial structure;
the heavy doping element A and the light doping element D are doped simultaneously, so that the occupation ratio of a generally expensive heavy element doping agent can be reduced, the material density is lightened, the discharge capacity of the material under the same compaction density is improved, and meanwhile, the production cost is reduced; the light doping element D can improve the structural stability of the polycrystalline anode material, is beneficial to outward diffusion of lithium ions and reduces internal resistance; the heavy doping element A has the effects of preventing primary particles from melting and refining grains, and is matched with pressurized oxygen sintering to realize surface micro-doping and cooperatively improve the morphology of secondary particles, so that gradient doping is achieved.
The cladding element L includes at least one of Li, al, W, ti, zr, sr, B, F; in the cladding layer, the doping element is obtained by outward diffusion of the doping element in the core layer, so that the cladding effect is improved, and the material consumption of the cladding agent is reduced.
The preparation is carried out in the pressurized oxygen atmosphere, so that the cross-section pore of the polycrystalline positive electrode material is reduced, the particle strength is improved, and when the cross-section porosity of the polycrystalline positive electrode material is within the range of 0.3-3%, the porosity is reduced, so that the polycrystalline positive electrode material can be promoted to enter a high-density state, and the material compaction density is improved.
In one technical scheme of the invention, the morphology of the core layer and the coating layer comprises secondary particles formed by aggregation of primary particles; and the primary particles and the secondary particles have radial structures; wherein, in the core layer, the light doping element D is distributed in the primary particles; the heavy doping element A is distributed on the outer surface of the primary particles; and the heavily doped element A permeates 2nm-20nm towards the inside of the primary particles on the outer surface of the primary particles.
Compared with the prior art, the technical effect achieved by adopting the technical scheme is as follows: primary particles refer to small irregular particles, also known as single crystals; the secondary particles are obtained by stacking primary particles, and are also called polycrystal; in the technical scheme provided by the invention, the core layer and the cladding layer are made of polycrystalline materials; in the core layer, the light doping element D is distributed in the primary particles; the heavy doping element A is distributed on the outer surface of the primary particle, and the heavy doping element A and the light doping element D serve as column ions, so that the micro-surface structure of the material can be enhanced, the stability of the material is improved, and the heavy doping element A permeates 2-20 nm into the primary particle on the outer surface of the primary particle.
In one aspect of the present invention, the primary particles have an aspect ratio in the range of 1 to 3; and/or the primary particles have an average grain size in the range of not more than 100nm 2 The method comprises the steps of carrying out a first treatment on the surface of the And/or Ni in secondary particles 3+ The ratio is not less than 98%; and/or the oxygen vacancies in the secondary particles do not exceed 1%.
Compared with the prior art, the technical effect achieved by adopting the technical scheme is as follows: the higher the oxidation state of the dopant, the better the improved cycle performance, which promotes the formation of a highly oriented, elongated microstructure, i.e., radial structure, which can maintain the integrity of the positive electrode material, inhibit the increase of resistance, and improve the cycle performance, so that when the aspect ratio of the primary particles is in the range of 1-3, the primary particles are defined as radial structures, and the polycrystalline positive electrode material has the best performance; and as the average grain size of the primary particles is not more than 100nm, the primary particles can be gathered more, the porosity is reduced, and the high-density state is promoted, so that the compaction density of the material is improved; ni in secondary particles 3+ The higher the Ni content in the positive electrode material, the higher the material capacity, and the higher the ratio is not less than 98%. The oxygen vacancy ratio in the secondary particles is not more than 1%, on one hand, lithium ions can borrow the oxygen vacancy, so that quick transmission is realized, and the rate capability of the material is improved; but since oxygen vacancies are not occupied by ions, if soThe structural stability of the material is reduced due to a large number of oxygen vacancies, grain boundary sliding is easy to occur, and intragranular cracks are caused, so that the electrochemical performance of the material is reduced, and the product performance is optimal.
In one embodiment of the invention, the content of doping elements in the polycrystalline positive electrode material in the core layer does not exceed 2wt.%; and/or in the core layer, the content of the light doping element D in the doping element is not less than 80wt.%; and/or the thickness of the coating layer is 1nm-100nm; and/or in the coating layer, the mass ratio of the heavily doped element A is not more than 5wt.%; and/or the weight ratio of the light doping element D in the coating layer is 1wt.% to 10wt.%.
Compared with the prior art, the technical effect achieved by adopting the technical scheme is as follows: in the nuclear layer, the content of the doping element in the polycrystalline anode material is not more than 2 wt%, the total mass ratio of the light doping element D in the doping element is not less than 80%, and the light doping element D has small atomic radius, low valence state, small electrostatic repulsive force and easy entering into the interior of primary particles; and the heavy doping element A is the opposite; meanwhile, in order to obtain the radial characteristic structure of the product, the high heavy doping element A duty ratio is needed, but the heavy doping element A duty ratio is not easy to enter the inside of the primary particles, so that the primary particles are enriched on the surface of the primary particles, and are prevented from being mutually swallowed and enlarged, so that the radial structure is obtained; in addition, the high-oxygen replaces heavy doping element A to be attached to the surface of the primary particles, so that the light doping element D can occupy a high ratio, the light doping element D is low in price, the structure is easier to stabilize in the nuclear layer, and the method is more suitable for industrial production.
The thickness of the coating layer is 1nm-100nm, in the coating layer, the mass ratio of the heavy doping element A is not more than 5 wt%, the mass ratio of the light doping element D is 1 wt% to 10 wt%, and the heavy doping element A and the light doping element D are obtained by outwards scattering bulk phase elements, so that the weight ratio in the coating layer is smaller, but a small amount of the heavy doping element A and the light doping element D can improve the coating effect, reduce the use of a coating agent and prevent the effect of mutual melting of primary particles.
In one aspect of the present invention,the particle D50 of the polycrystalline positive electrode material ranges from 8 mu m to 13 mu m; and/or the particle SPAN value of the polycrystalline positive electrode material is not less than 1.8; and/or the particle strength of the polycrystalline positive electrode material is not lower than 25mN; and/or the tap density of the polycrystalline positive electrode material is not less than 2.5g/cm 3 The method comprises the steps of carrying out a first treatment on the surface of the And/or the compacted density of the polycrystalline positive electrode material is not less than 3.2g/cm under a pressure of 2T 3 。
Compared with the prior art, the technical effect achieved by adopting the technical scheme is as follows: the particle D50, the particle SPAN SPAN, the particle strength, the tap density and the compaction density of the polycrystalline positive electrode material are high compaction, the particle SPAN SPAN value of the polycrystalline positive electrode material is not lower than 1.8, the particle strength of the polycrystalline positive electrode material is not lower than 25mN, and the tap density of the polycrystalline positive electrode material is not lower than 2.5g/cm through the fact that the particle D50 of the polycrystalline positive electrode material ranges from 8 mu m to 13 mu m 3 A compacted density of not less than 3.2g/cm of 1.5g of the polycrystalline positive electrode material under a pressure of 2T 3 The product performance effect is optimal under the proportion, and a high-compaction positive electrode material can be obtained.
In one technical scheme of the invention, the core layer has the composition shown in a formula (I): li (Li) y Ni a1 Co b1 Mn c1 A d1 D e1 O 2 Formula (I); in the core layer, the values of y, a1, b1, c1, d1, e1 are respectively as follows: y1 is more than or equal to 1 and less than or equal to 1.2,0.6, a1 is more than or equal to 1 and less than or equal to 0 and less than or equal to 0.3, c1 is more than or equal to 0 and less than or equal to 0.4, and d1 is more than or equal to 0 and less than 0.005;0 < e1 < 0.5;
the coating layer has the composition shown in formula (II): li (Li) y2 A d2 D e2 L f O 2 Formula (II); in the shell layer, the values of y2, d2, e2 and f are as follows: y2 is more than 0 and less than or equal to 1, d2 is more than 0 and less than 0.2; e2 is more than or equal to 0 and less than 0.1, and f is more than or equal to 0 and less than 1.
Compared with the prior art, the technical effect achieved by adopting the technical scheme is as follows: li, ni, co, mn is used as a matrix of the core layer, and the prepared anode material has better conductivity and higher theoretical capacity and conductivity; the synthesis process is simpler, the large-scale production, research and popularization can be realized, the material structure can be stabilized by adding Mn, the volume is prevented from being changed suddenly, the service life of the battery is prolonged, but the crystal structure still generates strain after repeated circulation by adding Mn, and the service life of the battery still cannot be optimized; co is added to further stabilize the crystal structure; the light doping element D can improve the structural stability of the polycrystalline anode material, is beneficial to outward diffusion of lithium ions and reduces internal resistance; the heavy doping element A has the effects of preventing primary particles from melting and refining grains, realizes surface micro doping by matching with pressurized oxygen sintering, and synergistically improves the morphology of secondary particles so as to achieve gradient doping
The method comprises the steps of taking oxides consisting of Li, a light doping element D, a heavy doping element A and a cladding element L as cladding layers, wherein the light doping element D and the heavy doping element A are obtained by outwards diffusing the light doping element D and the heavy doping element A in a core layer, so that the structural defects are repaired, the cladding effect is improved, the consumption of cladding agents is reduced, the material density cost is reduced, and the material capacity per unit weight is improved;
meanwhile, the light doped element D in the core layer is more to replace a large amount of heavy doped element A, so that the range of values of the heavy doped element A and the light doped element D in the core layer is more than 0 and less than 0.005;0 < e1 < 0.5; but the heavy doping element A is precipitated on the outer surface, and the heavy doping element A is more than the light doping element D in the shell layer, so that the value range of the heavy doping element A and the light doping element D of the shell layer is more than 0 and less than or equal to D2 and less than or equal to 0 and less than or equal to e2 and less than 0.1.
In order to achieve the second object of the present invention, the present invention provides a method for preparing a polycrystalline cathode material, the method comprising the steps of:
s100, mixing a precursor, a lithium source, a first doping agent containing a heavy doping element A and a second doping agent containing a light doping element D, and performing primary sintering treatment in a pressurized oxygen atmosphere to obtain a first oxide;
s200, mixing the first oxide with deionized water, and performing water washing treatment to obtain a first water-washed matter;
and S300, mixing the first water-washed matter with a coating agent containing a coating element L, and performing secondary sintering treatment under a pressurized atmosphere to obtain the anode material.
Compared with the prior art, the technical effect achieved by adopting the technical scheme is as follows: firstly, a precursor, a lithium source, a first doping agent containing heavy doping element A and a second doping agent containing light doping element D are mixed, primary sintering treatment is carried out under the pressurized oxygen atmosphere to obtain a first oxide, on one hand, the ion source can replace the traditional high-price heavy ion, the surface of primary particles is attached, the primary particles are prevented from being mutually fused, the grain refinement is completed, the formation of small and more primary particles is promoted, the small primary particles are favorable for the outward diffusion of lithium ions, and the internal resistance is reduced; on the other hand, the high-oxygen pressure energy reduces the atomic-level oxygen loss, inhibits the generation of oxygen vacancies and structural deformation, reduces the inter-crystal cracking and improves the structural stability of the material; meanwhile, the pressurized environment can promote the primary particles to shrink towards the core to form dense stacking, so that the particle stacking efficiency is improved, the porosity is reduced, the overall density and the particle strength of the secondary balls are improved, the formation of microcracks or cracks in the particles during charge and discharge cycles is reduced, and the material cycle performance is improved.
Secondly, the first oxide is mixed with deionized water, the first water-washed matter is obtained, impurities on the surface of the first oxide are cleaned after the water-washed matter is washed, a gap channel between primary particles is clear, and the method is favorable for enabling cladding elements to more easily penetrate into the gap channel of the primary particles under a pressurized high-temperature environment, so that uniform and effective cladding of the inner core is realized.
Mixing the first water-washed matter with a coating agent containing a coating element L, and performing secondary sintering treatment in a pressurized atmosphere to obtain a positive electrode material; after secondary sintering treatment, the structural defect is repaired, the coating effect is improved, the consumption of a coating agent is reduced, the material density cost is reduced, and the material capacity per unit weight is improved.
Further, in between S100 and S200, the method further includes crushing the first oxide; wherein the particle D50 of the first oxide obtained after the crushing treatment is in the range of 9-11 mu m; the crushing treatment can reduce agglomeration among the first oxides, so that the first oxides and the coating agent are mixed more fully, and the coating layer in the anode material is coated more uniformly.
In one embodiment of the present invention, in S100, the molar ratio of the precursor, the lithium source, and the first and second dopants is 1: (1.02-1.15): (0.001-0.01): (0.001-0.003); and/or in S200, the mass ratio of the first oxide to deionized water is 1: (0.5-1.5); and/or in S300, the molar ratio of the first water wash to the coating agent is 1: (0.001-0.005); in S100, the primary sintering treatment is performed in three sections, wherein the temperature of a first section is 500-600 ℃ and the time is 4-8 hours; the temperature of the second-stage temperature zone is 700-900 ℃ and the time is 10-18 h; the temperature of the three-stage temperature zone is 600-800 ℃ and the time is 3-6 h; and/or in S100, the pressure under the pressurized oxygen atmosphere is 3Mpa-15Mpa; and/or in S300, the temperature of the secondary sintering treatment is 400-600 ℃ and the time is 8-15 h; and/or in S300, the pressure under the pressurized atmosphere is 2Mpa to 15Mpa.
Compared with the prior art, the technical effect achieved by adopting the technical scheme is as follows: the composition ratio of the raw materials and the sintering process parameters relate to the size and the microscopic morphology of the cathode material, so that a preferred range is provided, and the implementation of the cathode material claimed in the application is facilitated for a person skilled in the art, wherein the molar ratio of the current precursor, the lithium source and the first and second dopants is 1: (1.02-1.15): (0.001-0.01): (0.001-0.003), wherein the mass ratio of the first oxide to the deionized water is 1: (0.5-1.5), the mole ratio of the first water washing matter to the coating agent is 1: (0.001-0.005), the primary sintering treatment is carried out in three sections, the temperature of the first section is 500-600 ℃ and the time is 4-8 h; the temperature of the second-stage temperature zone is 700-900 ℃ and the time is 10-18 h; the temperature of the three-stage temperature zone is 600-800 ℃ and the time is 3-6 h; when the temperature of the secondary sintering treatment is 400-600 ℃ and the time is 8-15 h, the product prepared by the proportion has the best performance effect and the optimal proportion, and is convenient for post-treatment.
Further, the step S100 is performed under the pressurized oxygen atmosphere, so that on one hand, the conventional high-valence heavy-mass ions can be replaced, the adhesion on the surfaces of the primary particles is realized, the mutual melting of the primary particles is prevented, the grain refinement is completed, and small and more primary particles are promoted; the small primary particles are beneficial to the outward diffusion of lithium ions and reduce the internal resistance; on the other hand, the pressurized environment can promote primary particles to shrink towards the core to form dense stacking, so that the particle stacking efficiency is improved, the porosity is reduced, the overall density and the particle strength of the secondary spheres are improved, the formation of microcracks or cracks in the particles during the charge-discharge cycle is reduced, the material cycle performance is improved, the atomic-level oxygen loss can be reduced under the pressurized oxygen atmosphere, the oxygen vacancy generation and the structural deformation are inhibited, the inter-crystal cracking is reduced, and the structural stability of the material is improved.
Step S300 is carried out in the pressurized oxygen atmosphere, so that the structural defect caused by crushing treatment can be repaired, the coating effect is improved, the consumption of a coating agent is reduced, the material density cost is reduced, and the material capacity per unit weight is improved.
To achieve the third object of the present invention, there is provided a lithium ion battery comprising the positive electrode material of any one of the above. Therefore, the technical scheme has the beneficial effects and is not repeated herein.
After the technical scheme of the invention is adopted, the following technical effects can be achieved:
(1) According to the method, the heavy doping element A and the light doping element D are doped at the same time, so that the occupation ratio of a generally expensive heavy element doping agent can be reduced, the material density is lightened, the discharge capacity of the material under the same compaction density is improved, and meanwhile, the production cost is reduced; the light doping element D can improve the structural stability of the polycrystalline anode material, is beneficial to outward diffusion of lithium ions and reduces internal resistance; the heavy doping element A prevents the primary particles from being mutually melted, completes grain refinement, promotes the formation of small and more primary particles, and simultaneously realizes surface micro-doping by matching with pressurized oxygen sintering, and cooperatively improves the morphology of the secondary particles so as to achieve gradient doping;
(2) The sintering is carried out in the pressurized oxygen atmosphere, so that on one hand, the traditional high-valence heavy-mass ions can be replaced, the adhesion on the surfaces of primary particles is realized, the mutual melting of the primary particles is prevented, the grain refinement is completed, and small and more primary particles are promoted; the small primary particles are beneficial to the outward diffusion of lithium ions and reduce the internal resistance; on the other hand, the pressurized environment can promote primary particles to shrink towards the core to form dense stacking, so that the particle stacking efficiency is improved, the porosity is reduced, the overall density and the particle strength of the secondary spheres are improved, the formation of microcracks or cracks in the particles during the charge-discharge cycle is reduced, the material cycle performance is improved, the atomic-level oxygen loss can be reduced under the pressurized oxygen atmosphere, the oxygen vacancy generation and the structural deformation are inhibited, the inter-crystal cracking is reduced, and the structural stability of the material is improved; in step S300, the structural defect caused by the crushing treatment can be repaired, the coating effect can be improved, the amount of the coating agent can be reduced, the material density cost can be reduced, and the material capacity per unit weight can be increased.
(3) The surface impurities of the first oxide can be cleaned by water washing treatment, the gap channels between the primary particles are clear, and the method is favorable for enabling cladding elements to permeate into the gap channels of the primary particles more easily under the pressurized high-temperature environment, so that the uniform and effective cladding of the inner core is realized.
Drawings
In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings to be used in the description of the embodiments will be briefly described below, it being obvious that the drawings in the following description are only some embodiments of the present invention, and that other drawings may be obtained according to these drawings without inventive effort for a person skilled in the art;
FIG. 1 is a surface topography of a polycrystalline positive electrode material according to embodiment 1 of the present invention;
FIG. 2 is a cross-sectional morphology of a polycrystalline positive electrode material according to embodiment 1 of the present invention;
FIG. 3 is a surface topography of a polycrystalline positive electrode material according to embodiment 3 of the present invention;
FIG. 4 is a graph showing the cycling capacity retention of the polycrystalline positive electrode materials of examples 1-2, comparative examples 1-7 at 3.0V-4.35V 1C/1C at 60℃according to the present invention;
FIG. 5 is a graph showing the rate of increase of cyclic DCR at 60℃for the polycrystalline cathode materials provided in examples 1-2, comparative examples 1-7, according to the present invention;
FIG. 6 is an initial DCR plot of the polycrystalline cathode materials provided in examples 1-2, comparative examples 1-7 at 3.0V-4.35V at 45℃at different SOCs according to the present invention.
Detailed Description
In order to make the above objects, features and advantages of the present invention more comprehensible, embodiments accompanied with present invention are described in detail with embodiments of the present invention including only some but not all embodiments. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.
Lithium ion (Li) + ) The battery is a secondary battery which mainly depends on Li + And moves between the positive electrode and the negative electrode to operate. During charge and discharge, li + To-and-fro intercalation and deintercalation between two electrodes: during charging, li + De-intercalation from the positive electrode, and intercalation into the negative electrode through the electrolyte, wherein the negative electrode is in a lithium-rich state; the opposite is true when discharging. Batteries generally employ materials containing lithium elements as electrodes, and lithium-containing positive electrode materials are representative of modern high-performance batteries.
In the research and development and preparation process of lithium ion batteries and positive electrode materials thereof, primary particles are mutually fused and become large, so that internal large gap residues are caused, and the problem of low circulation rate and stability of the lithium ion batteries is caused, so that how to improve the circulation rate and the low stability is always a target pursued by industry practitioners.
According to the method, fine primary particles are gathered more through pressurized oxygen, so that the porosity is reduced, the polycrystalline positive electrode material is promoted to be in a high-density state, the compaction density of the polycrystalline positive electrode material is improved, the rate capability of the polycrystalline positive electrode material is improved, and the stability of the polycrystalline positive electrode material is further improved.
Specifically, the invention provides a preparation method of a polycrystalline positive electrode material, which comprises the following steps:
s100, mixing a precursor, a lithium source, a first doping agent containing a heavy doping element A and a second doping agent containing a light doping element D, and performing primary sintering treatment in a pressurized oxygen atmosphere to obtain a first oxide;
s200, mixing the first oxide with deionized water, and performing water washing treatment to obtain a first water-washed matter;
and S300, mixing the first water-washed matter with a coating agent containing a coating element L, and performing secondary sintering treatment under a pressurized atmosphere to obtain the anode material.
Further, the precursor, the lithium source, the first doping agent containing the heavy doping element A and the second doping agent containing the light doping element D are mixed, primary sintering treatment is carried out under the pressurized oxygen atmosphere to obtain the first oxide, on one hand, the ion with high price and heavy mass can be replaced in the pressurized oxygen sintering environment, the adhesion of primary particles on the surface of the primary particles is realized, the mutual melting of the primary particles is prevented, the grain refinement is completed, small and more primary particles are promoted, the outward diffusion of lithium ions is facilitated by the small primary particles, and the internal resistance is reduced; on the other hand, the high-oxygen pressure energy reduces the atomic-level oxygen loss, inhibits the generation of oxygen vacancies and structural deformation, reduces the inter-crystal cracking and improves the structural stability of the material; meanwhile, the pressurized environment can promote the primary particles to shrink towards the core to form dense stacking, so that the particle stacking efficiency is improved, the porosity is reduced, the overall density and the particle strength of the secondary balls are improved, the formation of microcracks or cracks in the particles during charge and discharge cycles is reduced, and the material cycle performance is improved.
Preferably, the molar ratio of precursor, lithium source and first and second dopants is 1: (1.02-1.15): (0.001-0.01): (0.001-0.003); the primary sintering treatment is carried out in three sections, the temperature of a first section is 500-600 ℃ and the time is 4-8 hours; the temperature of the second-stage temperature zone is 700-900 ℃ and the time is 10-18 h; the temperature of the three-stage temperature zone is 600-800 ℃ and the time is 3-6 h; the pressure under the pressurized oxygen atmosphere is 3Mpa-15Mpa.
Further, a doping type precursor may be used, a doping element is added to the precursor to improve the doping effect, and a doping precursor or a batch process precursor may be used.
Preferably, the step of crushing the first oxide is further included between S100 and S200; wherein the particle D50 of the first oxide obtained after the crushing treatment is in the range of 9-11 mu m; the crushing treatment can enable the mixture between the first oxide and the coating agent to be more sufficient, and is favorable for the coating layer in the positive electrode material to be coated more uniformly.
Further, in S200, the mass ratio of the first oxide to deionized water is 1: (0.5-1.5), mixing the first oxide with deionized water, and performing water washing treatment to obtain a first water-washed object, wherein impurities on the surface of the first oxide are cleaned after the water washing treatment, and the gap channels between primary particles are clear, so that the coating elements can more easily permeate into the gap channels of the primary particles under the pressurized high-temperature environment, and the uniform and effective coating of the inner core is realized.
Further, in S300, the molar ratio of the first water-washed matter to the coating agent is 1: (0.001-0.005), the temperature of the secondary sintering treatment is 400-600 ℃, the time is 8-15 h, the pressure under the pressurized atmosphere is 2-15 Mpa, the first water-washed matter is mixed with the coating agent containing the coating element L, and the secondary sintering treatment is carried out under the pressurized atmosphere, so as to obtain the anode material;
furthermore, in S300, a small amount of flux may be added to improve the coating effect by sintering in cooperation with pressurized atmosphere, and after the secondary sintering treatment, the pressurized molten salt is coated on the outer surface of the core layer in a film shape, so as to repair the structural defect caused by the crushing treatment, improve the coating effect, reduce the consumption of the coating agent, reduce the material density cost and improve the material capacity per unit weight.
Specifically, the fluxing agent comprises SrO 2 、LiF、LiNO 3 、H 3 BO 3 、BF 3 At least one of them.
[ first embodiment ]
The embodiment provides a preparation method of a polycrystalline positive electrode material, which comprises the following steps:
s100, modifying NCM9055 precursor and LiOH.H 2 O、Al 2 O 3 、MoO 3 The molar ratio is 1:1.08:0.002: mixing at 0.0005 for one time, sintering at 550deg.C for 6 hr under 8Mpa pressurized oxygen atmosphere for one time, sintering at 770 deg.C for 12 hr for two-stage sintering, and sintering at 660 deg.C for 4 hr for three-stage sintering to obtain the first oxide；
S200, the mass ratio of the first oxide to deionized water is 1:0.5 adding the mixture into a water washing kettle, mixing for 30min, then adopting a filter press to remove water, and drying to finish water washing treatment to obtain a first water washing matter;
s300, mixing the first water washing with Al 2 O 3 And SrO 2 The molar ratio is 1:0.001: mixing materials at 0.0002, performing secondary sintering treatment at 400 ℃ for 10 hours under the oxygen atmosphere of 8Mpa, and cooling to obtain the anode material;
wherein after S100, the first oxide is cooled at room temperature and then mechanically crushed, controlling d50=10±1 μm; the surface morphology of the polycrystalline cathode material of this example is shown in fig. 1, and the cross-sectional morphology is shown in fig. 2.
[ second embodiment ]
This example provides a method for preparing a polycrystalline positive electrode material, the specific steps of which are described in example 1, with the difference that in S100, a modified NCM9055 precursor, liOH.H 2 O、MgO、WO 3 The molar ratio is 1:1.08:0.001:00002 are mixed once.
[ third embodiment ]
The specific steps of the preparation method of the polycrystalline cathode material are shown in example 1, wherein in S100, a precursor is mixed by using particles with the size of d50=13 μm and d50=3 μm, and the surface topography of the polycrystalline cathode material is shown in fig. 3.
[ fourth embodiment ]
The present embodiment provides a method for preparing a polycrystalline cathode material, with specific steps referred to in embodiment 1, except that in S100, a NM6535 precursor is used, and sintering is performed at 800 ℃ in an oxygen atmosphere.
[ fifth embodiment ]
The present embodiment provides a method for preparing a polycrystalline cathode material, wherein specific steps are shown in embodiment 1, and the difference is that each process parameter is selected, and specific process parameters are shown in table 1.
TABLE 1
[ sixth embodiment ]
This example provides a method for preparing a polycrystalline cathode material, specific steps are described in example 1, except that the content of each component is different, and specific steps are described in table 2.
TABLE 2
[ first comparative example ]
This comparative example provides a method for preparing a polycrystalline cathode material, specific steps of which are described in example 1, except that in S100, a sintering process is performed at 400 ℃ for 8 hours without a stepwise sintering process.
[ second comparative example ]
This comparative example provides a method for preparing a polycrystalline cathode material, specific steps of which are described in example 1, with the difference that in S200, a mass ratio of a first oxide to deionized water is 1:1.2, adding the mixture into a water washing kettle, stirring the mixture for 20 minutes, and then removing water by adopting a filter press.
[ third comparative example ]
This comparative example provides a method for preparing a polycrystalline cathode material, specific steps are described in example 1, except that in S300, the first water-washed matter is combined with Al 2 O 3 The molar ratio is 1:0.001 for mixing.
[ fourth comparative example ]
This comparative example provides a method for preparing a polycrystalline cathode material, specific steps are described in example 1, except that in S100, a modified NCM9055 precursor, liOH.H, is used 2 O、Al 2 O 3 The molar ratio is 1:1.08:0.002 was mixed once.
[ fifth comparative example ]
This comparative example provides a method for preparing a polycrystalline cathode material, see example 1, for specific steps, except that the preparation is performed under conventional oxygen pressure.
[ sixth comparative example ]
This comparative example provides a method for preparing a polycrystalline cathode material, see example 1 for specific steps, except that no S200 is used, i.e., no water wash.
[ seventh comparative example ]
This comparative example provides a method for preparing a polycrystalline cathode material, referring to example 1 for specific steps, except that in S300, the control air pressure is a standard atmospheric pressure.
The positive electrode materials obtained in examples 1 to 6 and comparative examples 1 to 7 were tested for the cycle capacity retention, DCR growth rate, cross-sectional porosity, tap density and particle strength, and various parameters were measured as shown in table 3;
specifically, the positive electrode materials obtained in examples 1 to 6 and comparative examples 1 to 7 have initial DCR values shown in Table 4 at different SOCs;
examples 1-2, comparative examples 1-7 provide polycrystalline positive electrode materials having a cycle capacity retention at 60 ℃ of 3.0V-4.35V 1C/1C as shown in fig. 4; examples 1-2, comparative examples 1-7 provide polycrystalline cathode materials with cyclic DCR growth rates at 60 ℃ as shown in fig. 5; examples 1-2, comparative examples 1-7 provide polycrystalline cathode materials having initial DCR at 3.0V-4.35V at 45 ℃ at different SOCs as shown in fig. 6;
TABLE 3 Table 3
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TABLE 4 Table 4
As can be seen from the comparison of example 2 and example 1, a better improvement effect can be achieved by appropriately changing the doping elements and the contents.
From a comparison of example 3 and example 1, it can be seen that the present application is equally applicable to the preparation of precursors having different particle sizes, and that a positive electrode material having better performance can be obtained.
As can be seen from a comparison of example 4 and example 1, a positive electrode material having good performance can be obtained even when cobalt is not contained in the precursor.
As can be seen from the comparison of the comparative example 1 and the example 1, the material has poor gas production performance without an annealing process, so that the addition of a proper annealing process is beneficial to improving the coating effect and reducing the defects between the coating layer and the core layer, thereby improving the gas production performance of the material.
As can be seen from the comparison of comparative example 2 and example 1, when the water washing strength is too high, the surface structure of the material is destroyed, which in turn causes deterioration of the material properties.
As can be seen from the comparison of comparative example 3 and example 1, the addition of a proper amount of fluxing agent is beneficial to improving the fire cladding effect and improving the material performance.
As can be seen from the comparison of comparative example 4 and example 1, adding a proper amount of heavy doping element can improve the surface doping and coating effect of the material, which is beneficial to improving the cycle and internal resistance performance of the material.
As can be seen from the comparison of comparative example 5 and example 1, the pressurized oxygen atmosphere is beneficial to improving the surface morphology of the material, reducing the loss of oxygen vacancies, and improving the compactness and compressive strength of the material, thereby improving the cycle performance of the material.
As can be seen from the comparison of comparative example 6 and example 1, the polycrystalline cathode material had a surface containing a large amount of Li after one sintering treatment 2 CO 3 And the impurities are directly coated without a water washing process, so that the coating effect is reduced, and the material performance is affected.
As can be seen from the comparison of comparative example 7 and example 1, the use of a pressurized atmosphere coating facilitates the improvement of the coating effect of the molten salt, thereby improving the gas generating properties of the material.
Finally, it should be noted that: the above embodiments are only for illustrating the technical solution of the present invention, and are not limiting; although the invention has been described in detail with reference to the foregoing embodiments, it will be understood by those of ordinary skill in the art that: the technical scheme described in the foregoing embodiments can be modified or some technical features thereof can be replaced by equivalents; such modifications and substitutions do not depart from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims (10)

1. A polycrystalline positive electrode material, characterized in that the polycrystalline positive electrode material comprises:
a core layer including an oxide containing Li, ni, a doping element;
a cladding layer that coats at least part of the surface of the core layer, and that includes an oxide containing Li, a doping element, and a cladding element L;
wherein the doping elements comprise a heavy doping element A and a light doping element D;
the light doping element D includes at least one of F, na, mg, al, ca; the heavily doped element a includes at least one of Ti, mo, W, ta; the cladding element L includes at least one of Li, al, W, ti, zr, sr, B, F;
in the cladding layer, the doping element is an out-diffusion result of the doping element in the core layer;
the polycrystalline positive electrode material has a radial structure, and the cross-sectional porosity of the polycrystalline positive electrode material ranges from 0.3% to 3%.
2. The polycrystalline positive electrode material according to claim 1, wherein,
the morphology of the core layer and the cladding layer comprises secondary particles formed by aggregation of primary particles; and the primary particles and the secondary particles have a radial structure;
wherein, in the core layer, the light doping element D is distributed within the primary particles;
the heavy doping element A is distributed on the outer surface of the primary particles;
and the heavily doped element A penetrates 2-20 nm from the outer surface of the primary particle to the inner part of the primary particle.
3. The polycrystalline positive electrode material according to claim 2, wherein,
the primary particles have an aspect ratio in the range of 1-3; and/or
The primary particles have an average grain size in the range of not more than 100nm; and/or
Ni in the secondary particles 3+ The ratio is not less than 98%; and/or
The oxygen vacancies in the secondary particles do not exceed 1%.
4. The polycrystalline positive electrode material according to claim 1, wherein,
in the core layer, the content of the doping element in the polycrystalline cathode material is not more than 2wt.%; and/or
In the core layer, the content of the light doping element D in the doping element is not less than 80wt.%; and/or
The thickness of the coating layer is 1nm-100nm; and/or
In the cladding layer, the light doping element D is present in a ratio of no more than 5wt.%; and/or
In the coating layer, the proportion of the heavily doped element A is 1wt.% to 10wt.%.
5. The polycrystalline positive electrode material according to claim 1, wherein,
the particle D50 of the polycrystalline positive electrode material ranges from 8 mu m to 13 mu m; and/or
The particle SPAN SPAN value of the polycrystalline positive electrode material is not lower than 1.8; and/or
The particle strength of the polycrystalline positive electrode material is not lower than 25mN; and/or
The tap density of the polycrystalline positive electrode material is not lower than 2.5g/cm 3 The method comprises the steps of carrying out a first treatment on the surface of the And/or
The compacted density of the polycrystalline positive electrode material is not less than 3.2g/cm under a pressure of 2T 3 。
6. The polycrystalline positive electrode material according to claim 1, wherein,
the core layer has a composition shown in a formula (I):
Li y Ni a1 Co b1 Mn c1 A d1 D e1 O 2 formula (I);
in the core layer, the values of y, a1, b1, c1, d1 and e1 are respectively as follows:
1.0≤y1≤1.2，0.6≤a1＜1，0≤b1≤0.3，0≤c1≤0.4，0＜d1＜0.005；0＜e1＜0.5；
the composition of the coating layer is shown as a formula (II):
Li y2 A d2 D e2 L f O 2 formula (II);
in the coating layer, the values of y2, d2, e2 and f are as follows:
0＜y2≤1，0＜d2＜0.2；0≤e2＜0.1，0＜f＜1。
7. a method for preparing a polycrystalline cathode material, characterized in that the method is used for preparing the polycrystalline cathode material according to any one of claims 1 to 6, the method comprising the steps of:
s100, mixing a precursor, a lithium source, a first doping agent containing a light doping element D and a second doping agent containing a heavy doping element A, and performing primary sintering treatment in a pressurized oxygen atmosphere to obtain a first oxide;
s200, mixing the first oxide with deionized water, and performing water washing treatment to obtain a first water-washed matter;
and S300, mixing the first water-washed matter with a coating agent containing a coating element L, and performing secondary sintering treatment under a pressurized atmosphere to obtain the polycrystalline positive electrode material.
8. The method according to claim 7, wherein,
in S100, the molar ratio of the precursor, the lithium source, and the first and second dopants is 1: (1.02-1.15): (0.001-0.01): (0.001-0.003); and/or
In S200, the mass ratio of the first oxide to deionized water is 1: (0.5-1.5); and/or
In S300, the molar ratio of the first water wash to the coating agent is 1: (0.001-0.005).
9. The method according to claim 7, wherein,
in S100, the primary sintering treatment is performed in three sections, wherein the temperature of a first section is 500-600 ℃ and the time is 4-8 hours; the temperature of the second-stage temperature zone is 700-900 ℃ and the time is 10-18 h; the temperature of the three-stage temperature zone is 600-800 ℃ and the time is 3-6 h; and/or
In S100, the pressure in the pressurized oxygen atmosphere is 3Mpa-15Mpa; and/or
In S300, the temperature of the secondary sintering treatment is 400-600 ℃ and the time is 8-15 h; and/or
In S300, the pressure in the pressurized atmosphere is 2Mpa-15Mpa.
10. A lithium ion battery comprising a polycrystalline positive electrode material according to any one of claims 1 to 6.
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